To have all extension associations, your user needs a full profile. As I know, no logonType is creating or loading the profile for you. Here I found something you might find of use: http://www.daniweb.com/software-development/csharp/threads/225868/how-to-programmatically-create-user-profile-c
]. Read all post carefully to copy the most complete code.
But I would not relay on associations. I would specify in a configuration file the CLSID needed for a specific extension, and look in the client registry for the application location, and start it passing the document as parameter. This way you don't need the complete profile, tehe interactive logon is enough.